• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 28
  • 5
  • 4
  • 2
  • Tagged with
  • 45
  • 45
  • 27
  • 23
  • 23
  • 20
  • 20
  • 20
  • 8
  • 6
  • 5
  • 5
  • 5
  • 5
  • 5
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Kinematic and dynamic analyses of cascades of planar four-bar mechanisms

Tsai, Der-Liang, 1958- January 1988 (has links)
Computer programs have been developed for the kinematic and dynamic analyses of cascades of planar four-bar mechanisms. Since the analytic approach has high efficiency and accuracy in computation, a chain of four-bar linkages is developed horizontally and vertically by using the relative coordinates and the absolute coordinates, from which the explicit equations and the simultaneous equations are respectively derived in the kinematic analysis. In this analysis, the actions of transmission of linkages, from left to right, from right to left and from lower to upper, are performed by the image method and transformation procedures. Based on the kinematic analysis, the dynamic analysis is also developed by using both sets of coordinate systems. The generalized equation of motion, the general form of Lagrange's equations, Lagrange multipliers and the theorem of power balance are used to construct various formulations of the governing equations of motion for some particular problems. The problem of a linkage with a moving frame (the ground link) is the most interesting focus in this analysis.

Electrodynamic forces in compensated pulsed electrical machines

Ozdemir, Muammer 10 June 2011 (has links)
Not available / text

Concurrent multiprocessors in computational mechanics for constrained dynamical systems

Kurdila, Andrew John 12 1900 (has links)
No description available.

Analysis of multi-branch torsional vibration for design optimization

Yao, Yuwen. January 2004 (has links)
Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains viii, 180 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 123-128).

Computational investigation of torque on spiral bevel gears

Rapley, Steve January 2009 (has links)
This thesis describes the development of a numerical modelling strategy for simulating the flow around a shrouded spiral bevel gear. The strategy is then applied to a series of parametric variations of key shroud parameters. The shroud and gear in question are generic, although based upon those employed in the internal gear box of a Rolls-Royce aeroengine. The need to shroud the gear comes from the fact that a spiral bevel gear, when rotated, acts like a fan. Work is done by the gear to move the surrounding fluid, usually air with oil particles suspended in it, which creates a parasitic loss, referred to as the windage power loss. The work within this thesis is part of a larger project which has investigated how windage power loss can be affected by geometric features of gears and shrouds. This is important as for large diameter (>200mm) bevel gears running at high speeds (>10,000 RPM) the windage power loss forms a substantial part of the total power loss. The modelling strategy has been developed in this work by studying 4 different fluid flow settings: Taylor-Couette flow, Conical Taylor-Couette flow, an unshrouded spiral bevel gear, and a shrouded spiral bevel gear. Work on Taylor-Couette flow provided a basic setting in which to trial various numerical techniques and gain familiarity with the commercial CFD program which would be used throughout this thesis (FLUENT), along with the meshing program GAMBIT. It gave an understanding of the flow, which was then used to simulate the flow in a modification of Taylor-Couette flow where the cylinders are replaced with cones, called Conical Taylor-Couette flow. Comparisons were made between 4 popular turbulence models, allowing a decision to be made on the `best' turbulence model to use in the modelling of a shrouded gear, and to start to develop the strategy. This strategy was then applied to the more complex geometry of an unshrouded gear, simulating experimental data which had been created on an in-house rig. To confirm the applicability of the strategy to modelling shrouded spiral bevel gears, it was applied to two shrouds for which experimental data was available. It showed that numerical modelling can capture the relative performance of the shrouds well. The work then continued by considering a series of parametric variations, whereby 3 key shroud parameters are each varied in 3 manners, producing 27 variations. Each of these parameters can affect the windage power loss: an assessment of how much each parameter affects windage power loss has been given. A description of the flow field in `good' and `bad' cases has been given, and through approximating the flow by using the compressible form of Bernoulli's equation, reasons for a `bad' shroud being `bad' have been presented.

Optimal control of a flywheel-based automotive kinetic energy recovery system

Ponce Cuspinera, Luis Alejandro January 2013 (has links)
This thesis addresses the control issues surrounding flywheel-based Kinetic Energy Recovery Systems (KERS) for use in automotive vehicle applications. Particular emphasis is placed on optimal control of a KERS using a Continuously Variable Transmission (CVT) for volume car production, and a wholly simulation-based approach is adopted. Following consideration of the general control issues surrounding KERS operation, a simplified system model is adopted, and the scope for use of optimal control theory is explored. Both Pontryagin's Maximum Principle, and Dynamic Programming methods are examined, and the need for numerical implementation established. With Dynamic Programming seen as the most likely route to practical implementation for realistic nonlinear models, the thesis explores several new strategies for numerical implementation of Dynamic Programming, capable of being applied to KERS control of varying degrees of complexity. The best form of numerical implementation identified (in terms of accuracy and efficiency) is then used to establish via simulation, the benefits of optimal KERS control in comparison with a more conventional non-optimal strategy, showing clear benefits of using optimal control.

Dynamic modeling, simulation and stability analysis of brushless doubly-fed machines

Li, Ruqi 02 May 1991 (has links)
A brushless doubly-fed machine (BDFM) is a single-frame, self-cascaded induction machine capable of operating in both the induction and the synchronous modes. This thesis presents some important advances concerning dynamic modeling, simulation and analysis of the BDFM. Initially, a two-axis model and its associated parameters are developed and calculated. The development of the model is not subject to the commonly made assumption that the BDFM is electromagnetically equivalent to two wound rotor induction motors in cascade connection. Instead, the model is derived from a rigorous mathematical transformation of a detailed machine design model. This novel approach emphasizes not only the analysis of the machine performance in both dynamic and steady state conditions, but also the design aspects of the machine by correlating the machine performance with the actual machine parameters computed from machine geometry. Using the two-axis model, simulation of the machine dynamic performance in all conceivable modes of operation is carried out and the results are compared with test data available with good correlation. Steady state models, under certain assumptions, are derived based on the two-axis model. For the synchronous mode, motoring operation, a solution technique is developed and utilized to perform steady state performance analysis of the BDFM. Finally, stability analysis of the machine is examined using the linearized version of the two-axis model. Since the linearized two-axis model of the BDFM is time-varying, commonly used eigenvalue analysis techniques cannot be employed directly to investigate the stability characteristics of the machine. However, since the system matrix is a periodic function of time, the theory of Floquet is introduced so that the original linear time-varying system of equations are transformed into a set of equivalent system of equations with a constant system matrix. Eigenvalue analysis is then applied to analyze the stability of the BDFM system over a wide speed range. Predictions by the eigenvalue analysis are correlated with test data. The study concludes that the proposed two-axis model is a good representation of the BDFM for dynamics, steady state, stability investigations of the machine and further development of control strategies for the proposed BDFM system for adjustable speed drive and variable speed generation applications. / Graduation date: 1991

Dynamic response of flexible rotating machines subjected to ground motions

Su, Wen-Chyi 30 November 1994 (has links)
Rotating machine play an important role in modern technology. Compressors in ventilating and cooling systems, pumps in power generation facilities, as well as high speed computer are all examples of flexible rotating machinery that must remain functional during and after a sever earthquake. Recent earthquakes have demonstrated that an aseismically designed structure may perform well during a strong earthquake yet still become nonfunctional due to damage in critical nonstructural components. For example, evacuation of several hospitals during the recent Northridge earthquake in the LA area was not caused by structural failure bur resulted from mechanical failure of the systems described above. Rotating machines are key components of such system. Further study into the behavior of these systems and technique for their protection for their protection during severe ground motion is needed. The flexible rotating machine is significantly complex, even for highly simplified models, due to gyroscopic and other effects. This paper presents the coupled, linear partial differential equations of motion of a flexible rotating shaft subjected to ground motion. Classical and finite element methods are developed to solve these equations. The effects of various physical parameters on the response of the system; magnitude, duration, and frequency content of the ground motion; bearing stiffness and damping; flexibility of the deformation and rotatory inertia effects are investigated, Both vertical and horizontal ground motion, individually and in combination, will be considered. / Graduation date: 1995

Robust rotordynamics

Rix, Andrew Iain James January 2016 (has links)
Vibration generated from main rotor unbalance has a major impact on the aerospace gas turbine industry. A combination of logistical and technological drivers differentiate aerospace gas turbines and their derivatives from other types of gas turbines with respect to the approach for managing vibration, leading to a bespoke approach for the design, build, and balancing. The key drivers are: limited accessibility to rotors within the engine, the requirement for exchangeable modules (sub-assemblies) of major parts of the rotor without rebalancing, the use of only low-speed balancing on pseudo-rigid rotors with bladed assemblies, very low vibration limits leading to very tight balancing limits, extreme weight limits for design solutions, and the need for highly accurate, repeatable, and stable rotor joints. This study proposes and demonstrates a novel and rapid robust design system that has been created to deal with these unique challenges. The system comprises an overarching process and a set of novel tools and methods that have been created to support the process. These tools comprise an Unbalance Response Function (URF) design method that effectively delivers a preliminary design assessment and a fast Monte-Carlo simulation and comparison method with supporting software for comparing and improving build and balance design solutions. The aim of the overall process is to generate a system that identifies and controls critical parameters, and alleviates time wasted controlling non-critical parameters. The target outcome is therefore the most cost effective, predictable and repeatable solution with respect to rotor generated vibration (i.e. robust). Two novel methods of informing and improving the outcome of the low-speed balancing process using extra information available about the rotor are also introduced.

An experimental study of lifting and moving forces in air conveying systems

Chardon, Sylvaine 06 October 2009 (has links)
An air conveying system uses pressurized air as a propelling force to lift and move articles. It is supplied by a fan into a plenum with a top surface that is a flat perforated plate. Air escapes through the openings, creating a layer that supports and drives the articles along. This thesis provides information on the lifting and moving forces. It summarizes the results of both analytical and experimental studies. Most of the effort is focused on an experimental procedure for measuring the actual forces on the objects being conveyed and data are used to verify the analytical models. The experiments are limited to straight holes and louvers located under the bottom of aluminum concave-bottom cans. In some tests, a flat disc has been fixed to the bottom of the cans. Measurements are made of the can motion on an actual section of conveyor. / Master of Science

Page generated in 0.0768 seconds